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Primary genotypic resistance of HIV-1 to the maturation inhibitor PA-457 in protease inhibitor-experienced patients

Malet, Isabellea; Wirden, Marca; Derache, Annea; Simon, Anneb; Katlama, Christinec,d; Calvez, Vincenta; Marcelin, Anne-Genevièvea

doi: 10.1097/QAD.0b013e3280b079d9
Research Letters

Sequences from 82 protease inhibitors (PI)-experienced patients were analysed for the presence of previously described in-vitro resistance mutations to PA-457 located in the C-terminal capside (H226Y, L231F, L231M) and in the N-terminal SP1 (A1V, A3T, A3V) within the CA-SP1 boundary domain. Overall, the CA-SP1 cleavage site was highly conserved in PI pre-treated patients and only one patient showed an L231M mutation. The impact of this mutation should be further addressed in vivo.

aLaboratoire de Virologie, Université Pierre et Marie Curie (Paris 6), France

bService de Médecine Interne, France

cService des Maladies Infectieuses, Hôpital Pitié-Salpêtrière, Assistance Publique-Hôpitaux de Paris, Paris, France

dINSERM U720, Université Pierre et Marie Curie (Paris 6), Paris, France.

Received 7 December, 2006

Accepted 15 December, 2006

The maturation inhibitor PA-457 (3-O-{3′,3′-dimethylsuccinyl}-betulinic acid) represents a new substance class for the treatment of HIV infection. It is a small molecule inhibitor of late-stage HIV-1 replication cycle that acts by specifically disrupting the conversion of the Gag capside precursor protein (p25CA-SP1) to mature capside protein (p24CA) resulting in the release of immature, non-infectious virus particles [1]. In vitro, serial passage experiments identified six single amino acid substitutions that independently confer PA-457 resistance: three at or near the C terminus of capside (CA-H226Y, L231F, and L231M) and three at the first and third residues of SP1 (SP1-A1V, A3T, and A3V) [2]. In vivo, preliminary results in eight HIV-1-infected patients treated by PA-457 in monotherapy (200 mg once a day) for 10 days reported an HIV-1 plasma viral load decrease of −1.1 log10 copies/ml [3].

In antiretroviral-naive patients there is a limited degree of natural polymorphism at the CA-SP1 cleavage site in subtype B HIV-1 because only one position has been reported to be polymorphic, V362I, which is present in 7% of naive patients [4].

In protease inhibitor (PI)-experienced patients, the resistance to PI follows an accumulation of mutations in the viral protease, mostly located in the active site of the enzyme and therefore having impact on protease activity [5]. It has thus been shown that compensatory Gag cleavage site mutations allow an increase of the enzymatic activity and a partial recovery in producing mature infectious virions [6,7]. These mutations are usually described in the two sites NC/p1 and p1/p6 [8], and even outside of the Gag cleavage site [9]. Currently, there is a lack of information on the possibility of mutations in the CA-SP1 cleavage site in PI-experienced patients. As mutations in this site, selected in vitro in serial passage experiments with PA-457, could impair the activity of this drug, it is important to know whether primary resistance to PA-457 can be detected in patients previously exposed to PI before the initiation of PA-457.

In this report, sequences of the entire CA-SP1 boundary domain (GHKARVLAEAMSQVTNPATIM) from 82 PI-experienced patients infected with subtype B HIV-1 strains were analysed for the presence of previously described in-vitro mutations linked to resistance to PA-457.

At the time of analysis, patients were treated by at least two nucleoside reverse transcriptase inhibitors and one PI, and harboured virological failure with a mean HIV-1 plasma viral load of 4.44 ± 0.75 log10 copies/ml (mean ± standard deviation). The mean duration of exposure to antiretroviral therapy was 46 ± 36 months and to PI was 24 ± 15 months. According to the 2006 International AIDS Society – USA panel (, the baseline median number of major and minor PI mutations was two (zero to six) and six (one to 12), respectively.

Viral RNA was extracted from plasma samples and the reverse transcriptase–polymerase chain reaction followed by a second round polymerase chain reaction were performed as previously described [10]. The following primer pairs were used: [nucleotides (nt) 1585–1610] 5′–ATAATCCTGGGATTAAATAAAATAGT–3′ and (nt 2093–2114) 5′–TTGTAGGAAGGCCAGATCTTCC–3′ as outer primers, and (nt 1747–1766) 5′–ACCTTGTTGGTCCAAAATGC–3′ and (nt 2023–2047) 5′–CTTCCTTTCCACATTTCCAACAGCC–3′ as inner primers. The 301 base pair region covering the CA-SP1 boundary sequence was purified using Amicon Microcon-100 (Millipore Corporation, Billerica, Massachusetts, USA) and sequenced using a cycle sequencing reaction with the Big Dye terminator kit (Applied Biosystems, Foster City, California, USA). The sequences were aligned using Sequence Navigator software.

Twenty-one amino acids of the CA-SP1 boundary domain from the 82 sequences were compared with the HxB2 reference sequence (Table 1). The sequence analysis showed a total conservation for nine out of the 21 amino acid residues analysed (43% of conservation). The conserved positions are particularly located in the C-terminal capside (H226, K227, A228, R229) and in the N-terminal half of SP1 (A1, E2, A3, M4). The M14 position, also highly conserved, is located in the extremity of the C-terminal of SP1 that is separated from the two other conserved regions. On the other hand, a high degree of variability has been observed in the C-terminal half of SP1 (Q6 to I13). In the conserved region, among the 82 sequences analysed, V230I has been identified in eight patients (10%) and a particular mutation, L231M, in one patient. The past history of treatment of this patient who harboured the L231M mutation was no different from the other patients studied.

Table 1

Table 1

The results of this study show that the CA-SP1 cleavage site seems to be highly conserved in PI-pretreated patients. As determinants of PA-457 activity are limited mostly to C-terminal capside and the N-terminal half of SP1 [11], these results are comforting for the use of this drug in PI-pretreated patients. The V230I mutation, located in the C-terminal capside, is present in 10% of PI-pretreated patients, which is similar to what has previously been described in naive patients. Although CA-SP1 resistance mutations to PA-457, such as L231M, could be observed in one patient previously exposed to PI, this seems to be a rare event. The L231M mutation has been identified in in-vitro drug-resistance selection studies with PA-457 and confers some level of resistance to PA-457, suggesting that this residue plays a critical role in mediating the effect of the compound on CA-SP1 processing. The impact of this mutation should, however, be further addressed in vivo.

Moreover, HIV-1 subtypes are geographically distributed, with subtype B predominating in north America and Europe. Consequently, the bulk of studies on the biological basis of drug susceptibility have been undertaken on subtype B viruses. The most prevalent viruses worldwide are, however, non-B, and the prevalence of non-B viruses is increasing in Europe [12,13]. Genetic subtypes may influence drug susceptibility, as well as the likelihood of developing drug resistance-associated mutations. Currently, there is a lack of information on primary resistance of HIV-1 to PA-457 in different HIV-1 subtypes, suggesting the need for such studies.

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